Negative-acting no-process printing plates

ABSTRACT

A photosensitive composition is prepared containing a polymer of the formula B(X)(Y) wherein B represents an organic backbone, each X independently is an acidic group or salt thereof and each Y independently is a photocurable group and a photoinitiating compound or compounds. Preferably, free-radically polymerizable multi-functional monomer and/or oligomer is added to the photosensitive composition. The photosensitive composition can be coated on a suitable substrate for planographic printing plate applications. Imagewise irradiation causes the light struck regions to photocure, becoming insoluble in aqueous and organic mediums, while the non-light struck regions remain highly soluble/dispersable. Printing plates of this construction do not require processing prior to being run on a press.

This application is a division of U.S. application Ser. No. 08/811,022,U.S. Pat. No. 5,925,497 filed Mar. 4, 1997, which is a division of U.S.application Ser. No. 08/582,459, filed Jan. 3, 1996, abandoned, which isa continuation-in-part of U.S. application Ser. No. 08/429,899, filedApr. 27, 1995, abandoned.

FIELD OF THE INVENTION

In one aspect, this invention relates to novel photosensitivecompositions. In another aspect, this invention relates tonegative-acting printing plates prepared from the novel photosensitivecompositions. This invention further relates to a method of use for thenovel printing plates that requires no further processing steps afterexposure and prior to placing the printing plates on press.

BACKGROUND OF THE ART

The production of lithographic plates is well-known in the graphic artsindustry. Lithographic processes generally employ at least two steps toprepare a plate for use in a printing press, namely exposure of a platecoated with a photosensitive composition to a light source through amask (e.g., a positive or a negative mask), thus creating a photoimage,and a subsequent development step. Presensitized plates which are basedon aluminum or polyester sheet-like material and are consideredplanographic in nature are commonly used in the industry. Typically, ina negative-acting system, the exposed areas become insolubilized (e.g.,polymerized or crosslinked), and the development step involves washingmaterial away from the unexposed portions of the plate. Conversely, in apositive-acting system, the development step involves washing materialaway from the exposed portions of the plate. The development stepusually involves rinsing and washing with a developer solution and oftenis performed in a processing unit containing the developer solution. Thedeveloper solution generally is highly alkaline and often contains anorganic solvent, such as benzyl alcohol. Alternatively, development ofthe photoimage has sometimes been accomplished by heating.

Both of the above-described (i.e., wet and thermal) developmentprocesses suffer from the drawback of being relatively time-consumingand expensive in some instances. Furthermore, when volatile organic orstrongly alkaline solutions are employed as developer solutions,disposal of these solutions presents an environmental problem.

A printing plate which does not require processing prior to press wouldbe desirable to the printing industry not only for environmentalreasons, but also because it would reduce cost, reduce pressroom space,and decrease make-ready time. Because of these issues, the industry haslong sought photosensitive compositions which do not have theabove-described drawbacks. One method of overcoming these drawbacks isto provide a lithographic printing plate which does not requiredevelopment or processing between imaging and being run on press. Theterm “no-process” as used herein refers to a printing plate which doesnot require any treatment, mechanical or chemical, between exposure andbeing run on press.

Constructions of positive-acting plates which do not require processingafter imaging and before being run on press have been disclosed (e.g.,see U.S. Pat. Nos. 5,102,771; 5,225,316 and 5,314,785). These patentsdisclose printing plates which are based on a photosensitive coatingcontaining an ester of acrylic or methacrylic acid polymer and aphotoacid-generating system. Upon imagewise exposure to actinicradiation, the polymer decomposes in the light struck regions, becomingfountain receptive, while areas in the non-light struck areas remain inkreceptive.

Presensitized negative-acting lithographic plates which do not requireprocessing after imaging and before being run on press are also known inthe art. A category of plates which do not require processing betweenimaging and being run on press are described in U.S. Pat. Nos.3,231,378; 3,285,745; and 3,409,487. These plates contain aphotosensitive composition comprising a phenolic resin, an ethyleneoxide polymer, and a photosensitizer. Upon exposure to actinicradiation, radicals are generated which cause the oxidation of thephenolic resin, thereby increasing the ink receptivity. A drawback ofthese plates is their tendency to become less ink receptive during theprinting process. The loss of ink receptivity requires tight control ofink/water balance on press and, additionally, can cause the plates tobecome inoperable. U.S. Pat. No. 3,793,033 discloses the incorporationof hydroxyethylcellulose ether in the construction. The resultant platesdid not suffer from blinding (i.e. loss of image on printing) andrequired less control of ink/water balance on press. A significantdisadvantage of this construction is the use of phenolic resins whichrequire curing to achieve suitable run lengths on press. The curingrequirements necessitate a two layer system with the sensitizer appliedon top of the phenolic-containing layer after the phenolic layer hasbeen cured. If the sensitizer is not coated after curing, it candecompose during the cure step.

Another category of negative-acting plates which do not requireprocessing between imaging and being placed on press are those based onmultiple photosensitive layers. Typically, these constructions have ahydrophilic photosensitive layer nearest the substrate and an additionallayer which is capable of photohardening in conjunction with the firstlayer, as described, for example in U.S. Pat. Nos. 4,600,679 and4,104,072 and European Pat. Publ. No. 450,199. Constructions such asthese generally employ a negative-acting photosensitive compositionbased on aromatic diazo compounds as the hydrophilic layer closest tothe substrate. A disadvantage is that these plates have a tendency toscum (i.e. take ink in the background areas) and also to contaminate theprinting press. This drawback requires that plates first be washed witha suitable washing agent (i.e. fountain) prior to being run on press.Therefore, the incorporation of diazo compounds and resins todeleterious to the performance of plates intended for use as“no-process” plates. Printing plates are disclosed in PCT ApplicationNo. 93-05446 in which the diazo components have been eliminated from thehydrophilic layer, thus eliminating the problem of press contaminationassociated with residual unreacted diazo materials. The described plateis comprised of a plate/base substrate, a photosensitive polymerichydrophilic layer nearest the base, and a separate photosensitivepolymeric hydrophobic layer being next closest to the substrate. Thephotosensitive hydrophilic layer is based on polymerizable materialswhich do not contain diazo compounds. The functionality of the plate isderived from the insolubilization and hardening of both layers uponexposure to actinic radiation. This plate only requires a press equippedwith ink and fountain to achieve good prints after exposure without theneed to pre-wash the plate prior to being run on press. Because thisconstruction has an external hydrophobic layer, it is impractical toachieve roll-ups equal to conventional plates without some treatment toremove the hydrophobic material from the background areas prior to beingrun or press.

It was against this background that the present invention dealing withnegative-acting lithographic printing plates which require no furtherprocessing steps after exposure and prior to being placed on press wasdeveloped. These plates are prepared from a photosensitive compositioncomprising a reactive, acid functional polymer.

Reactive, acid functional polymers for a processed flexographicapplication have been disclosed in U.S. Pat. No. 5,268,257. In thepreparation of flexographic printing plates, a relatively thick coating(typically 1-2 mm) of a flexible, photosensitive polymer is applied to aflexible substrate. During processing, a relief image is formed on theplate through exposure and wet development of the plate. The flexible,reactive, acid functional polymers disclosed in U.S. Pat. No. 5,268,257are prepared by reacting a flexible carboxylated copolymer with aphotosensitive vinyl containing compound, followed by an optionalmaleation reaction to increase the level of acid group functionality.Polymers prepared by this method result in a maximum acid groupfunctionality of less than 0.37 ephr (equivalents per hundred gram ofresin) and a maximum vinyl group functionality of less than 0.13 ephr.

SUMMARY OF THE INVENTION

The novel photosensitive composition of the present invention comprises:(a) a reactive, acid functional polymer of the formula B(X)(Y), whereinB represents an organic backbone, each X independently is an acidicgroup or salt thereof present in an amount of between 0.02 and 0.8 ephr,and each Y independently is a photocurable group present in an amount ofbetween 0.35 and 1.0 ephr; and (b) a photoinitiator which initiatescrosslinking of the reactive, acid functional polymer upon exposure toradiation. It is emphasized that X can also represent the salt of anacid group generated through the addition of appropriate organic orinorganic base such as NaOH, Na₂CO₃, (CH₃CH₂CH₂CH₂)₄N⁺OH⁻, etc.

In a preferred embodiment, the photosensitive composition furthercomprises free-radically polymerizable multi-functional monomer and/oroligomer in order to increase the photospeed and durability of thephotosensitive composition in printing plates and other applications.

In another embodiment of the present invention, a negative-actingprinting plate is provided which comprises a substrate coated with aphotosensitive composition comprising: (a) a reactive, acid functionalpolymer of the formula B(X)(Y), wherein B represents an organicbackbone, each X independently is an acidic group or salt thereof andeach Y independently is a photocurable group; and (b) a photoinitiatorwhich initiates crosslinking of the reactive, acid functional polymerupon exposure to radiation, wherein X and Y are present in an amountsufficient to enable the printing plate to be placed directly on pressafter exposure with no additional processing steps being required.

In a further embodiment, the process of the invention involves theformation of an imaged article (e.g., printing plate) comprising thesteps of: (a) exposing a negative-acting printing plate (as disclosedearlier herein) to radiation (e.g., within a range absorbed by aphotoinitiator or sensitized photoinitiator present in the printingplate) to form a latent image-bearing article; (b) thereafter on press,applying a fountain solution to the latent image-bearing article; and(c) applying ink to the latent image-bearing article, thereby forming animaged article. An alternative to the above process involves contactingthe latent image-bearing article with a dye instead of ink to form animaged article.

In an alternative embodiment, the process of the invention involves theformation of an imaged article (e.g., printing plate) comprising thesteps of: (a) exposing a negative-acting printing plate (as disclosedearlier herein) to radiation (e.g., within a range absorbed by aphotoinitiator or sensitized photoinitiator present in the printingplate) to form a latent image-bearing article; and (b) thereafter onpress, applying an emulsion comprising fountain solution and ink to thelatent image-bearing article, thereby forming an imaged article.

The photosensitive compositions of the present invention can betransparent or alternatively, translucent or opaque by the addition ofsuitable levels of opacifying pigment.

Preferred reactive, acid functional polymers of the present invention offormula B(X)(Y) are those in which each X is a carboxyl group or saltthereof and each Y contains an ethylenically-unsaturated group that canbe polymerized by a free-radical mechanism. The number average molecularweight of the above polymers are preferably between about 1000 and500,000, and more preferably, between about 2,000 and 50,000. Thepreferred level of polymerizable ethylenically-unsaturated groups Y inthe above polymers is between 0.35 and 1.0 ephr, more preferably between0.4 and 0.9 ephr, and most preferably between 0.45 and 0.8 ephr; and thepreferred level of the acidic X group is between 0.02 and 0.8 ephr, morepreferably between 0.05 and 0.6 ephr, and most preferably between 0.1and 0.4 ephr.

Optionally, the photosensitive composition may also include a colorantand/or dye or dye/sensitizer system which upon exposure to light changescolor. Additionally, the present photosensitive composition may containvarious materials (e.g., stabilizers, surfactants, organic or inorganicbeads, etc.) in combination with the essential ingredients of thepresent invention.

The construction of the negative-acting no-process printing plates ofthe present invention differs significantly from those known in the art.The construction of the present invention consists of a singlephotosensitive layer on a substrate. Additionally, the photosensitivelayer does not contain phenolic resins or diazo/diazo based compounds.Finally, unlike conventional and flexographic printing plates, the plateof the present invention does not require any treatment after exposureprior to being run on press.

Other aspects, advantages, and benefits of the present invention areapparent from the detailed description, examples, and claims.

DETAILED DESCRIPTION OF THE INVENTION

The construction of the present invention comprises a photosensitivelayer which further comprises a crosslinkable polymer and aphotoinitiator which, upon exposure to radiation, initiates crosslinkingof the polymer. Optionally, the photosensitive composition may alsoinclude a colorant and/or dye or dye/sensitizer system which uponexposure to light changes color. Additionally, the presentphotosensitive composition may contain various materials (e.g.,stabilizers, surfactants, etc.) in combination with the essentialingredients of the present invention. Said photosensitive layer iscoated on a suitable substrate.

Polymers of the photosensitive composition of this invention have thegeneral formula B(X)(Y), wherein B represents an organic backbone, eachX independently is an acidic group or salt thereof and each Yindependently is a photocurable group. These polymers are similar instructure to those disclosed in U.S. Pat. No. 5,130,347 for use infilled dental cement containing reactive powders.

Preferably the backbone B is an oligomeric or polymeric backbone ofcarbon-carbon bonds, optionally containing non-interfering substituentssuch as oxygen, nitrogen or sulfur heteroatoms. The term“non-interfering” as used herein refers to substituents or linkinggroups which do not unduly interfere with the photocrosslinkingreaction.

Preferred X groups are carboxyl groups and salts thereof Suitable Ygroups include, but are not limited to, polymerizableethylenically-unsaturated groups. Ethylenically-unsaturated groups arepreferred, especially those that can be polymerized by means of afree-radical mechanism, examples of which are substituted- andunsubstituted-acrylates, methacrylates, alkenes and acrylamides. X and Ygroups can be linked to the backbone B directly or by means of anynon-interfering organic linking group, such as substituted orunsubstituted alkyl, alkoxyalkyl, aryl, aryloxyalkyl, alkoxyaryl,aralkyl, alkaryl, ester, or amide groups.

Preferred precursors to polymers of formula B(X)(Y) are polymers orcopolymers having the structure B(X). The precursor polymers orcopolymers B(X) suitable for this reaction are those which have a highamount of acid functionality, preferably 0.75-1.6 ephr. The term “ephr”refers to the equivalents of functional groups per 100 grams of resin(e.g., polymer B).

Photocrosslinkable polymers of formula B(X)(Y) can be prepared accordingto a variety of synthetic routes. The preferred method consists ofreacting a polymer of formula B(X) with a suitable coupling compound inorder to form pendent Y groups. Y groups are therefore incorporated bythe use of a “coupling compound” (i.e. a compound containing both a Ygroup and a reactive group capable of reacting with the polymer throughan X group). The product of the reaction between the coupling compoundand the X group thereby links the Y group to the backbone in a pendentfashion. This reaction may take place with the evolution of a gas, suchas CO₂. Suitable coupling compounds are organic compounds, optionallycontaining non-interfering substituents and/or non-interfering linkinggroups between the Y groups and the reactive group. Polymers of formulaB(X)(Y) which are useful in this invention are those in which the levelof polymerizable ethylenically-unsaturated groups Y is preferablybetween 0.35 and 1.0 ephr, more preferably between 0.4 and 0.9 ephr, andmost preferably between 0.45 and 0.8 ephr; and the level of the acidic Xgroup is preferably between 0.02 and 0.8 ephr, more preferably between0.05 and 0.6 ephr, and most preferably between 0.1 and 0.4 ephr.

Preferred photocrosslinkable polymers of formula B(X)(Y) are those inwhich each X is a carboxyl group or salt thereof and each Y contains anethylenically-unsaturated group that can be polymerized by afree-radical mechanism. Such polymers are conveniently prepared byreacting a polyalkenoic acid (e.g. polymers of the formula B(X), whereineach X is a carboxyl group or salt thereof) with a coupling compoundcontaining both a polymerizable ethylenically-unsaturated group and agroup capable of reacting with the carboxylic acid group. The numberaverage molecular weight of the resultant photocrosslinkable polymer ispreferably between 1000 and 500,000, and more preferably between 2,000and 50,000. These polymers are generally water dispersable (e.g.,soluble, swellable, etc.), but to a lesser extent than the polyalkenoicacids from which they are derived.

Suitable polyalkenoic acids for use in preparing the photocrosslinkablepolymers of the present invention include homopolymers and copolymers ofunsaturated mono-, di-, or tricarboxylic acids. Preferred polyalkenoicacids are those prepared by the polymerization and copolymerization ofunsaturated aliphatic carboxylic acids, for example, acrylic acid,2-chloroacrylic acid, 3-chloroacrylic acid, 2-bromoacrylic acid,3-bromoacrylic acid, methacrylic acid, itaconic acid, glutaconic acid,aconitic acid, citraconic acid, mesaconic acid, fumaric acid, and tiglicacid. Suitable monomers which can be copolymerized with the unsaturatedcarboxylic acids include unsaturated aliphatic compounds, such asacrylamide, acrylonitrile, vinyl chloride, allyl chloride, vinylacetate, and 2-hydroxyethyl methacrylate. Other monomers or comonomersthat may be used include N-acryloyl or N-methacryloyl derivatives ofamino acids. Examples of suitable amino acids are glycine;glycylglycine; alanine; valine; leucine; isoleucine; phenylalanine;tyrosine; proline; hydroxyproline; serine threonine;3-amino-3-methylbutanoic acid; 6-aminocaproic acid; aminobenzoic acid(meta and para); 4-aminosalicylic acid; iminodiacetic acid; lanthionine;methionine; aspartic acid; glutamic acid; lysine; delta-aminolevulinicacid; beta-alanine; alpha-aminobutyric acid; gamma-aminobutyric acid;gamma, epsilon-diaminopimelic acid; alpha, gamma-diaminobutyric acid;ornithine; omega-aminododecanoic acid; beta-cyanoalanine;epsilon-methylhistidine; canavanine; jenkolic acid; 1-azaserine;gamma-methylene glutamic acid; N-methyl tyrosine; arginine; tryptophan;norvaline; cystine; cysteine; and hydroxylysine.

Particularly preferred polyalkenoic acids are the homopolymers andcopolymers of acrylic, methacrylic, and itaconic acids. Polymers of theformula B(X) can thus be prepared by copolymerizing an appropriatemixture of monomers and/or comonomers. Preferably, the polymers areprepared by free-radical mechanism in solution, emulsion or interfacialmethods. Such polymers can then be reacted with coupling compounds inthe presence of catalysts as described below.

Coupling compounds suitable for use in preparing the preferred polymersof the present invention include compounds which contain at least onegroup capable of reacting with X in order to form a covalent bond, aswell as at least one polymerizable ethylenically-unsaturated group. WhenX is carboxyl, a number of groups are capable of reacting with X,including both electrophilic and nucleophilic groups. Examples of suchgroups include the following moieties: —OH, —NH₂, —NCO, —COCl, and

Examples of suitable coupling compounds include, but are not limited to,acryloyl chloride, methacryloyl chloride, vinyl azlactone, allylisocyanate, 2-hydroxyethylmethacrylate, 2-aminoethylmethacrylate, and2-isocyanatoethyl methacrylate. Other examples of suitable couplingcompounds include those described in U.S. Pat. No. 4,035,321. Examplesof preferred coupling compounds include, but are not limited to, thefollowing methacrylates and their corresponding acrylates and allylcompounds.

Particularly preferred coupling compounds are the followingmethacrylate, its acrylate analog and allyl compounds:

Preferred photocrosslinkable polymers of formula B(X)(Y) are prepared byreacting a polymer of formula B(X) wherein X is COOH with an isocyanatefunctional coupling compound. The resultant polymers of formula B(X)(Y)are then those where Y is linked to the X group by an amide linkage.Therefore, the amount (e.g., in ephr) of Y groups incorporated can becontrolled by varying the equivalents of coupling compounds containing Yfunctional groups added to the polymer B(X). Thus, the composition ofthe photoactive polymer can be varied over a wide range. The preferredamount of Y groups in polymers of formula B(X)(Y) is 0.35-1.0 ephr,which can be calculated from the equivalents of coupling compoundsreacted with polymer of formula B(X). The particularly preferred amountof Y groups is 0.45-0.8 ephr.

The polymer of the present invention may comprise between about 99.99%and 60% of the photosensitive layer. Preferably the polymer comprisesbetween about 98% and 70% of the layer, more preferably between about97% and 80% of the photosensitive layer.

In a preferred embodiment of the present invention, multifunctionalmonomers/oligomers are added to the photosensitive composition.Non-limiting examples of such monomers/oligomers are (meth)acrylic acidesters such as ethyl acrylate, butyl acrylate, allyl acrylate,multifunctional acrylates and methacrylates such as zinc diacrylate,1,6-hexanediol diacrylate, pentaerythritol triacrylate andtetraacrylate, 1,3,5-tri-(2-acryloyloxyethyl)isocyanurate, propoxylatedglyeryl triacrylate, ethoxylated trimethylolpropane triacrylate,polyethylene glycol dimethylacrylate, and derivatives of isocyanatocontaining ethylenically unsaturated compounds reacting with water,diols and polyols dicarboxylic acids and polycarboxylic acids. Examplesof the isocyanato monomers are 2-isocyanatoethyl methacrylate anddimethyl-m-isopropenyl benzyl isocyanate. An example of the reaction ofan isocyanatocontaining ethylenically unsaturated compound with water isthe reaction product of 2-isocyanatoethyl methacrylate with water,1,3-bis(2′-methyacryloxyethyl)urea (e.g.,CH₂═C(CH₂)—CO—OCH₂CH₂NH—CO—NHCH₂CH₂—CO—O—C(CH₃)═CH₂.

When utilized, the total amount of multifunctional monomers/oligomerspresent in the photosensitive layer is from about 0.1 to about 90 wt %of the layer, more preferably between about 5 to 50 wt % of the layer.

The term “photoinitiator”, as used herein, refers to any compound orcombination of two or more components which upon exposure toelectromagnetic radiation are capable of accelerating crosslinking ofthe above described polymers. The photoinitiator may be either a singlecompound or a combination of two or more components. Photoinitiatorswhich initiate crosslinking due to the production of free-radicals uponexposure are preferred. Preferred photoinitiators are active whenexposed to radiation between 200 and 1200 nm (e.g., ultraviolet,visible-light and infra-red radiation). Particularly preferredphotoinitiators are active in the range of 300 to 850 nm.

Examples of suitable visible light- and ultraviolet-inducedphotoinitiators include, but are not limited to, ketones such as benziland benzoin, and acyloins and acyloin ethers, for example2,2-dimethoxy-2-phenylacetophenone (Irgacure® 651),2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone(Irgacure® 369) and benzoin methyl ether(2-methoxy-2-phenylacetophenone), all commercially available fromCiba-Geigy Corp.; sensitized diaryliodonium salts and triarylsulfoniumsalts (described, for example, in U.S. Pat. Nos. 3,729,313; 4,058,400;4,058,401; 4,460,154; and 4,921,827). Suitable sensitizers for thediaryliodonium and trialrysulfonium salts are described in the foregoingpatents. Preferred photoinitiators include chromophore-substitutedhalomethyl-1,3,5-triazine compounds, such as those described in U.S.Pat. Nos. 3,987,037; 4,476,215; 4,826,753; 4,619,998; 4,696,888;4,772,534; 4,189,323; 4,837,128; and 5,364,734, and halomethyloxadiazoles such as those described in U.S. Pat. No. 4,212,970. All suchphotoinitiators can be used alone or with suitable accelerators (e.g.,amines, peroxides, and phosphorous compounds) and/or with suitablephotosensitizers (e.g., ketone or alpha-diketone compounds such ascamphorquinone).

The photoinitiator is preferably present in the construction of thepresent invention in an amount sufficient to achieve the desired extentof polymerization. Such amount is dependent on the efficiency of thephotoinitiator and the thickness of the photoactive layer. Typically aphotoinitiator will be present in an amount of about 0.01% to 20% byweight of the coating. The preferred amount of photoinitiator in thepresent invention is 0.5% to 15% by weight of the coating and aparticularly preferred amount being between 0.5% to 10%.

An optional component of the lithoplate described in this invention is acolorant and/or dye or dye system. The visible image colorant and/or dyeor dye system is not essential to the invention, however, it isgenerally desired to have a visible image after exposure and thus acolorant and/or dye or dye system may be added. Compounds or systemssuitable for use are those which change color or hue upon exposure toactinic radiation or upon contact with the products from the exposedphotoinitiator. Suitable compounds or systems include, but are notlimited to leuco dyes, such as acyl protected thiazines, diazines andoxazines, hydrols (e.g., Michler's Hydrol), indolinenes andtriarylmethane lactones (e.g., Crystal Violet Lactone). Preferred dyesused in the plate construction are substituted triarylmethane type leucodyes. The dye is preferably present in the lithographic plate of thepresent invention in an amount sufficient to achieve the desiredcontrast between exposed and unexposed portions of the plate. Preferredlevels of the dye are between 0 and 10% of the coating weight.

Additionally, the present photosensitive composition may contain variousmaterials in combination with the essential ingredients of the presentinvention. For example, pigments, organic or inorganic beads,sensitizing dyes, plasticizers, binders, surfactants, antioxidants,coating aids, anti-static agents, waxes, ultra-violet or visible lightabsorbers and brighteners may be used without adversely affecting thepractice of the invention.

Photosensitive compositions of the present invention are normally coatedby means known in the art (e.g., knife coating, blade coating, barcoating, roll coating, extrusion coating, etc.) onto a substrate. Thephotosensitive composition is applied to the appropriate substrate at acoating weight of 0.01 g/m² (1 mg/ft²) to 5.38 g/m² (500 mg/ft²).Particularly preferred coating levels of the photosensitive layer arebetween 0.33 g/m² (30 mg/ft²) and 1.94 g/m² (180 mg/ft²).

Suitable substrates on which the photosensitive composition may becoated include but are not limited to, metals or metal alloys, forexample steel and aluminum plates, sheets or foils including aluminumtreated with hydrophilic agents, such as silicates or polyacrylic acidand its derivatives; films or plates composed of various film-formingsynthetic or high polymers including addition polymers (e.g.,poly(vinylidene chloride), poly(vinyl chloride), poly(vinyl acetate),polystyrene, polyisobutylene polymers and copolymers), and linearcondensation polymers (e.g., poly(ethylene terephthalate),poly(hexamethylene adipate), poly(hexamethylene adipamide/adipate));paper or paper laminates. Aluminum and aluminum alloys are preferredsubstrates. Aluminum or aluminum alloys which have been silicated areparticularly preferred.

Additionally, it may be desired to apply an additional non-photoactivelayer on top of the photosensitive layer. Examples of such layersinclude, but are not limited to polymers and laminated films, such aspolyester.

The following non-limiting examples further illustrate the presentinvention.

EXAMPLES

Acrylic acid, itaconic acid, polyacrylic acid (MW=2,000), triphenylantimony, dibutyl tin dilaurate, allyl isocyanate, and3,5-di-t-butyl-4-hydroxytoluene (BHT) were obtained from AldrichChemical Co. (Milwaukee, Wis.) and used as such. Polyacrylic acid(“PAA”) (mw=50,000) was obtained from Polysciences (Warrington, Pa.) ina 25% aqueous solution. The aqueous solution was dried to remove waterand the solid residue was taken up and then precipitated from THF/ethylacetate to obtain the solid material used in the examples below. Theterm “IEM” means 2-isocyanato ethyl methacrylate and was obtained fromShowa Denka (Japan) and Polysciences (Warrington, Pa.) and used as such.The term BHT means 3,5-di-t-butyl-4-hydroxytoluene. The term AIBN means1,1′-azobis(isobutyronitrile) (available from Kodak and DuPont). Theterm “MOSTOL” means 2,4-bistrichloromethyl-6-[p-(2-hydroxyethoxy)styryl-1,3,5-triazine] asdescribed in U.S. Pat. No. 4,476,215. The term “XL Leuco” means[bis(4-dimethylamino-2-methylphenyl)-4-dimethylaminophenyl]methane whichwas prepared in a manner similar to the general method described in Fr.Pat. No. 1,406,247. KC-4 is the amino ketone substituted coumarinsensitizer:

which was prepared as described in European Pat. Publ. No. 538,997. Theterm IPA means isopropyl alcohol or isopropanol. The term THF meanstetrahydrofuran.

Materials were analyzed by one or more of the following techniques: ¹HNMR, infrared, and mass spectroscopy; gel phase chromatography; anddifferential scanning calorimetry. Aluminum substrates used for coatingsin the following experiments were cleaned, degreased lithograde alloy,electrochemically grained, anodized and silicated aluminum sheets.Exposures were conducted using either a Berkey Ascor vacuum frameexposure unit (Berkey Technical Co., Woodside, N.Y.; equipped witheither an Addalux Lamp No. 1406-01 or an Addalux Supercharged 5 kWTriplespectrum Lamp No. 754-18017) or a Burgess vacuum frame (BurgessIndustries, Minneapolis, Minn., equipped with a 5 kW TriplespectrumMetal Halide Lamp). A neutral density 21 step (0.15 absorbanceunits/step) sensitivity guide (Stouffer Graphic Arts Equipment Co.,South Bend, Ind.) was used to measure the photosensitivity of thecoatings prepared below.

The term solid step as used below refers to the highest numbered stepwhich is completely inked after the imaged plate is run on press or handinked. The term open step refers to the highest numbered step which iscompletely free of ink after the imaged plate is run on press or handinked. Press results were obtained using either a Ryobi 3200 ACD, aHeidelberg SORMZ, a Harris LTV or a Didde Apollo press. The presses wereequipped with Viking® Fountain with IPA or suitable alcohol replacement.An additional method used to identify the printability of the plates washand inking using Rub-Up™ Ink U-62 (Printing Development, Inc., Racine,Wis).

Example 1

This example describes the preparation of a copolymer of acrylic acidand itaconic acid wherein the molar ratio of acrylic acid to itaconicacid is 3:1.

A glass reactor equipped with an addition funnel, a reflux condenser anda dry nitrogen air inlet tube was charged with 150 mL dry THF (watercontent<0.005%) and 13.0 g of itaconic acid (0.10 mol). The reactionvessel was kept under an atmosphere of nitrogen throughout theprocedure. The mixture was stirred and the acid dissolved after severalminutes. A solution of acrylic acid (21.6 g, 0.30 mol) in 35 mL of THFwas then added to the reactor. A solution of AIBN in dry THF was thenadded to the stirring reaction mixture such that 2% by weight based onthe total weight of the monomers of AIBN was added. The reaction wasmaintained at room temperature for 30 min and then refluxed for 18 hrresulting in a homogeneous, slightly hazy solution. When a drop of thereaction mixture was added into several mL of ethyl acetate,precipitation of a white polymer was observed. The polymer wascalculated to have 1.45 ephr acid functionality.

Example 2

This example describes the reaction of a copolymer of acrylic acid anditaconic acid (3:1 molar ratio) with IEM wherein the motor ratio of IEMto acid groups in the copolymer 0.8:1.

The resultant solution of Example 1 was maintained at a bath temperatureof about 40-50° C. under an atmosphere of dry air. A solution containing0.4 g BHT, 0.4 g triphenylantimony, and 3.4 g dibutyltin dilaurate in 20mL of dry THF was slowly added to the stirring copolymer solution. IEM(55.6 g, 0.4 mol) was then added dropwise to the mixture over a periodof approximately 1 hr. After the IEM addition was complete, the reactionsolution was stirred for approximately 18 hr at a bath temperature ofapproximately 40-50° C. until the evolution of carbon dioxide ceased andthe solution became homogeneous. Infrared spectral analysis showed theabsence of the NCO band at about 2300 cm⁻¹. A white polymer wasprecipitated by the slow addition of the reaction mixture which had beenpreviously diluted with three times its volume of ethyl acetate tohexanes. After precipitation a white solid was isolated and dried undervacuum. The yield of the polymer was approximately 96%. The polymer wascalculated to have 0.14 ephr acid functionality and 0.55 ephrpolymerizable ethylenically-unsaturated functionality.

Example 3 (Comparative Example)

A copolymer of acrylic acid and itaconic acid was prepared as in Example1 except that the molar ratio of acrylic acid to itaconic acid was 4:1.The polymer was calculated to have 1.44 ephr acid functionality. Theresulting polymer was reacted with IEM as described in Example 2, exceptthat the molar ratio of IEM to acid groups was 0.16:1. The resultingpolymer was isolated by precipitation from ethyl acetate. The polymerwas calculated to have 0.96 ephr acid functionality and 0.18 ephrpolymerizable ethylenically-unsaturated functionality.

Examples 4-6

These examples describe the reaction of polyacrylic acid (mw=2,000,calculated 1.39 ephr acid functionality) with IEM wherein the molarratio of IEM to acid groups ranges from 0.5:1 to 0.8:1.

A glass reactor was equipped with an addition funnel, a refluxcondenser, a dry air inlet tube and 75 mL of dry THF (watercontent<0.005%). Polyacrylic acid (mw=2,000, 8.64 g, 0.12 mol acidgroups) was added to the flask. After stirring at a bath temperature of50-70° C. for 2-3 hr, a cloudy solution was obtained. The temperature ofthe bath was maintained at 40-50° C. and a solution containing 0.093 gBHT, 0.093 g triphenylantimony, and 0.64 g dibutyltin dilaurate in 5 mLof dry THF was slowly added to the stirring polymer solution. IEM thenwas added dropwise to the mixture over a period of 0.5-1.5 hr. Theamount of IEM added for each example is listed in Table I. After addingthe IEM, the mixture was stirring continuously overnight. The completionof the reaction was monitored by the disappearance of NCO band around2300 cm⁻¹. White solid polymers were obtained by precipitation with thesolvent indicated. After isolation, the white solids were dried undervacuum. The solvents used for precipitation and the yields of thepolymers isolated are reported in Table I.

TABLE I Molar Poly- Ex- IEM, IEM, Ratio Precipitation Acid, Unsat., merample g mole IEM:Acid Solvents ephr ephr Yield 4 14.9 0.096  0.8:1Hexane 0.12 0.50 90% 5 12.1 0.078 0.65:1 Petroleum 0.24 0.45 92% Ether 69.3 0.060  0.5:1 Petroleum 0.39 0.39 90% Ether

Examples 7-8

These examples describe the reaction of polyacrylic acid (mw=50,000,calculated 1.39 ephr acid functionality) with IEM wherein the molarratio of IEM to acid groups is 0.5:1 and 0.8:1.

A glass reactor was equipped with an addition funnel, a refluxcondenser, a dry air inlet tube and 75 mL of dry THF (water content<0.005%). Polyacrylic acid (mw=50,000, 8.64 g, 0.12 mol acid groups) wasadded to the flask. After stirring at a bath temperature of 50-70° C.for 2-3 hr, a cloudy solution was obtained. The temperature of the bathwas maintained at 40-50° C. and a solution containing 0.093 g BHT, 0.093g triphenylantimony, and 0.64 g dibutyltin dilaurate in 5 mL of dry THFwas slowly added to the stirring polymer solution. IEM then was addeddropwise to the mixture over a period of 0.5 hr. The amount of IEM addedto each example is listed in Table II. After adding the IEM, the mixturewas stirred continuously overnight. The completion of the reaction wasmonitored by the disappearance of NCO band around 2300 cm⁻¹. White solidpolymers were obtained by precipitation with the solvents indicated.After isolation, the white solids were dried under vacuum. The solventsused for the precipitation and the yields of the polymers isolated arereported in Table II.

TABLE II Molar Poly- Ex- IEM, IEM, Ratio Precipitation Acid, Unsat., merample g mole IEM:Acid Solvents ephr ephr Yield 7 14.9 0.096 0.8:1Hexane/ 0.12 0.50 85% Ethyl Acetate (5:1) 8 9.3 0.060 0.5:1 Ethyl 0.390.39 80% Acetate

Example 9

This example describes the reaction of polyacrylic acid (mw=2,000,calculated 1.39 ephr acid functionality) with allyl isocyanate whereinthe molar ration of allyl isocyanate to acid groups is 0.8:1.

A glass reactor was equipped with an addition funnel, a reflux condenserand a dry air inlet tube and 50 mL of dry THF (water content<0.005%).Polyacrylic acid (mw=2,000, 8.64 g, 0.12 mol acid groups) was added tothe flask. After stirring at a bath temperature of 60° C. for 1 hr, acloudy solution was obtained. The temperature of the bath was maintainedat 40-50° C. and a solution containing 0.093 g BHT, 0.093 gtriphenylantimony, and 0.64 g dibuyltin dilaurate in 2 mL of dry THF wasslowly added to the stirring polymer solution. A solution of allylisocyanate (8.0 g, 0.096 mol) in 8 mL of THF then was added over aperiod of 30 min. The reaction solution was stirred continuouslyovernight and became clear brown in color. The completion of thereaction was monitored with the disappearance of NCO band around 2300cm⁻¹. The viscous solution was diluted with THF and precipitated with a1:3 mixture of hexanes/ethyl acetate. A fine white powder was isolatedand dried giving a polymer yield of 48%. The polymer was calculated tohave 0.19 ephr acid functionality and 0.77 ephr polymerizableethylenically-unsaturated functionality.

Example 10

This example describes the preparation of polyacrylic acid (calculated1.39 ephr acid functionality) and subsequent reaction with IEM whereinthe ratio of IEM to acid groups is 0.8:1.

A glass reactor was equipped with an addition funnel, a reflux condenserand a gas inlet tube. The reaction vessel was purged with dry nitrogenand then charged with 70 mL of dry THF (water content<0.005%) andacrylic acid (7.2 g, 0.10 mol). The reaction solution was maintainedunder an atmosphere of nitrogen. After stirring for 30 min, a solutionof 0.029 g AIBN in 5 mL of THF was added to the reaction solution. Thesolution was heated to and maintained at a bath temperature of 65° C.overnight. After stirring overnight, the reaction solution was placedunder an atmosphere of dry air and the temperature of the bath wasmaintained at 40°50° C. A solution containing 0.10 g BHT, 0.10 gtriphenylantimony, and 0.850 g dibutyltin dilaurate in 5 mL of dry THFwas slowly added to the stirring polymer solution. IEM (12.41 g, 0.08mol) was then added dropwise to the mixture over a period of 0.5 hr.After adding the IEM, the mixture was stirred continuously overnight.The completion of the reaction was monitored by the disappearance of NCOband around 2300 cm⁻¹. A white polymer was precipitated by the additionof the reaction mixture which had been previously diluted with threetimes its volume of ethyl acetate to hexanes. After precipitation, thewhite solid was dried under vacuum. The polymer was calculated to have0.12 ephr acid functionality and 0.50 ephr polymerizableethylenically-unsaturated functionality.

Example 11

This example describes the preparation of a printing plate with materialfrom Example 9.

A coating solution containing 1.06 g of the solid product of Example 9,0.072 g MOSTOL, 0.072 g XL Leuco, and 8.8 g 1-methoxy-2-propanol(Dowanol PM) was prepared. The solution was coated on anelectrochemically grained, anodized and silicated aluminum substrateusing a #6 wire wrapped rod (R&D Specialities, Webster, N.Y.). The platewas dried with a heat gun and exposed through a negative film in aBerkey Ascor vacuum frame for 70 sec. After exposure, the plate was handinked using rub ink and Viking® fountain with 10% IPA. The exposed areasof the plate accepted ink and unexposed areas excluded ink. A solid step4 on the Stouffer gray scale was observed for the inked plate.

Examples 12-15

These examples describe the preparation of printing plates withmaterials from Examples 2, 4, 7 and 8. Solutions were prepared accordingto Table III.

TABLE III Amt of Example Polymer Polymer MOSTOL XL Leuco Dowanol PM 12Example 4 1.056 g 0.072 g 0.072 g 8.8 g 13 Example 7 1.056 g 0.072 g0.072 g 8.8 g 14 Example 8 1.056 g 0.072 g 0.072 g 8.8 g 15 Example 21.056 g 0.072 g 0.072 g 8.8 g

The solutions were coated on an electrochemically grained, anodized andsilicated aluminum substrate using a #6 wire wrapped rod (R&DSpecialties, Webster, N.Y.). The plates were then dried for 2 min at 75°C. The plates then were exposed through a negative film in a Burgessvacuum frame for 24 units. The plates were mounted on an Apollo pressequipped with Kohl Madden, T81-7015 ink (tack 12) and Viking® fountainwith 10% IPA under yellow lights. The press was then started and theprinted solid steps, the speed of the roll-up, and the number ofimpressions printed before the samples were removed from the press wererecorded. Roll-up as used herein is defined as the number of impressionsbefore a clean copy (i.e. fully inked image and fully clean background)is obtained. A roll-up which is termed “fast” is generally equivalent tothe roll-up observed on a processed conventional plate. The data issummarized in Table IV.

TABLE IV Example Roll-up 1st Solid Step Impressions printed 12 Fast 1060,000 13 Fast 10 40,000 14 Fast  6 40,000 15 Fast 11 60,000

Example 16

This examples describes the preparation of a printing plate preparedusing material from Example 10.

A coating solution containing 0.470 g of the solid product of Example10, 0.030 g, Irgacure® 369 (Ciba-Geigy), and 4.5 g 1-methoxy-2-propanol(Dowanol PM) as prepared. The solution was coated on anelectrochemically grained, anodized and silicated aluminum substrateusing a #6 wire wrapped rod (R&D Specialties, Webster, N.Y.). The platewas dried with a heat gun and exposed through a negative film in aBerkey Ascor vacuum frame for 70 sec. After exposure, the plate was handinked using rub up ink and Viking® fountain with 10% IPA. The exposedareas of the plate accepted ink and the unexposed areas excluded ink.

Examples 17-19

These examples describes the preparation of a printing plate suitablefor imaging with 488 and 532 nm light and prepared with material fromExample 4.

A coating solution containing 0.820 g of the solid product of Example 4,0.020 g KC-4, 0.160 g diphenyliodonium hexafluorophosphate, and 9.0 g1-methoxy-2-propanol (Dowanol PM) was prepared. The solution was coatedon an electrochemically grained, anodized and silicated aluminumsubstrate using a #6 wire wrapped rod (R&D Specialties, Webster, N.Y.).The plate was dried with a heat gun and exposed through a negative filmwith a 3M Model 70 exposure unit equipped with a tungsten lamp. Severallight filters were used to determine the response of the plate tovarious wavelengths of light. The exposure conditions and theprintability are summarized in Table V. Printability is used to describea plate which takes ink in the imaged areas and excludes ink from thenon-imaged areas. Printability was determined by hand inking the exposedplates with rub up ink and Viking® fountain with 10% IPA.

TABLE V Example Filter Exposure (units) Printability 17 None  2 Good 18532 nm band pass 120 Good 19 488 nm band pass 120 Good

Example 20

This example describes the preparation of a printing plate preparedusing polymer from Example 2 and a pigment.

A coating solution containing 124.5 g of a polymer prepared in a similarfashion to Example 2, 9.0 g MOSTOL, 9.0 g XL Leuco, 32.6 g magentamillbase pigment (23% solids, prepared as described in copending U.S.patent application Ser. No. 08/402,628, filed Mar. 15, 1995), and 1324.9g 1-methoxy-2-propanol (Dowanol PM) was prepared. The solution wascoated by extrusion on an electrochemically grained, anodized andsilicated aluminum substrate at a coating weight of 129 g/m² (120mg/ft²).

One plate of this example was exposed through a negative film in aBurgess vacuum frame for 24 units. After exposure the plate was mountedon a Heidelberg SORMZ press equipped with Viking® fountain with 10% IPAand INX Inc. o/s Riegel 2 Process™ Black ink. The exposed area startedto accept ink after 2 impressions the unexposed area showed a cleanbackground after 200 impressions.

Another plate of this example was exposed through a negative film in aBurgess vacuum frame for 12 units. After exposure the plate wasprocessed in a 3M 1132 processor equipped with Viking® plate developer.The processed plate was mounted on a Harris press equipped with KohlMadden, MSP-61235-A ink and Viking® fountain with 25% IPA. The plategave a good roll-up and printed greater than 10,000 impressions.

Example 21

This example describes the preparation of a printing plate preparedusing polymer from Example 2.

A coating solution containing 0.2 g of a polymer prepared in a similarfashion to Example 2, 0.014 g MOSTOL, 0.014 g Pergascript Turquoise(Ciba-Geigy), and 1.76 g 1-methoxy-2-propanol (Dowanol PM) was prepared.The solution was coated on an electrochemically grained, anodized andsilicated aluminum substrate using a #6 wire wrapped rod (R&DSpecialties, Webster, N.Y.). The plate was dried with a heat gun andexposed through a negative film in a Berkey Ascor vacuum frame for 1minute. After exposure, the plate was hand inked using rub up ink andViking® fountain with 10% IPA. The exposed areas of the plate acceptedink and the unexposed areas excluded ink.

Example 22 (Comparative Example)

This example describes the preparation of a printing plate preparedusing polymer from Example 3.

A coating solution containing 1.056 g of the polymer of Example 3, 0.072g MOSTOL, 0.072 g XL-leuco, and 8.8 g 1-methoxy-2-propanol (Dowanol PM)was prepared. The solution was coated on an electrochemically grained,anodized and silicated aluminum substrate using a #6 wire wrapped rod(R&D Specialties, Webster, N.Y.). The plate was dried with a heat gunand exposed through a negative film in a Berkey Ascor vacuum frame for70 seconds. After exposure, the plate was hand inked using rub up inkand Viking® fountain with 10% IPA. No solid step was obtained. The inkreceptivity of the exposed area was poor.

Example 23

This example describes the preparation of a printing plate preparedusing polymer from Example 6.

A coating solution containing 1.056 g of the polymer of Example 6, 0.072g MOSTOL, 0.072 g XL-leuco, and 8.8 g 1-methoxy-2-propanol (Dowanol PM)was prepared. The solution was coated on an electrochemically grained,anodized and silicated aluminum substrate using a #6 wire wrapped rod(R&D Specialties, Webster, N.Y.). The plate was dried with a heat gunand exposed through a negative film in a Berkey Ascor vacuum frame for70 seconds. After exposure, the plate was hand linked using rub up inkand Viking® fountain with 10% IPA. The exposed area accepted ink welland eight solid steps were obtained.

Example 24

The following coating solutions were prepared:

Component A B PAA (polymerized in 0.4% AIBN)- 0.88 g (100%) 1.80 g (90%)IEM (80%) MOSTOL 0.080 g (4%) XL LEUCO 0.120 g (6%) Dowanol PM 9.1 g18.0 g

C: To 4.0 g of B was added 0.018 g of tetramethylammonium hydroxidepentahydrate (5% of the polymer).

D: To 3.0 g of A was added 0.015 g of tetramethylammonium hydroxidepentahydrate (5% of the polymer).

The solutions were coated on 16M base with #6 meyer rod. The coating wasdried by blowing a hot air gun over it for a few seconds. The plateswere aged at 60° C., for 0, 1, 2, and 3 days. After the aging, the platewas exposed in a Berkey Ascor vacuum frame for 70 sec. then inked withVIKING® fountain. The results were as follows:

fresh 1 day 2 days 3 days Image Backg'd Image Backg'd Image Backg'dImage Backg'd A no clean no clean no clean no clean B 9 f.s.st. cleanNA* scummed NA scummed NA scummed C 6 f.s.st. clean 6 f.s.st. clean 6f.s.st. clean 7 f.s.st. clean D no clean no clean no clean no cleanf.s.st.: first solid step Backg'd: background *: not readable due to thescumming

Example 25

The following solutions were prepared:

Component A (standard) B-G PAA (polymerized with 2% 85% of total solid75% AIBN)-IEM (70%) MOSTOL 4% 4% XL LEUCO 6% 6% tetramethylammonium 5%5% hydroxide pentahydrate multifunctional monomers* 0% 10% Dowanol PM10% solid content 10% solid content *multifunctional monomers/oligomerswere as follows: B: ethyoxylated trimethyolpropane triacrylate (SR454)C: propoxylated trimethyolpropane triacrylate (SR492) D: ethyoxylatedtrimethyolpropane triacrylate (SR9035) E: propoxylated glyceryltriacrylate (SR9020) F: polyethylene glycol 100 - dimethylacrylate G:polyethylene glycol 1000 - dimethylacrylate

The solutions were coated on EC grained, anodized and silicated basewith #6 meyer rod. The coating was dried at 80° C./2 min. The plateswere exposed to Berkey Ascor for 10 units then run on a press withoutany previous wet development. All the plates were quickly rolled up witha high contrast image and a clean background. The relative press-life ofthe plates compared with the standard plate (A) is listed below.

A B C D E F G Δ(1st solid step)* 0 +1 +1 +1 +1 +2 +2 relativepress-life** 100% 250% 150% 150% 250% 100% 50% *Δ(1st solid step) = (#of the 1st solid step on print sheet after 100 impressions) − (# of the1st solid step on print sheet after 100 impressions of A) **relativepress-life = (# of impressions of the experimental plate/# ofimpressions of A) × 100%

Reasonable variations and modifications are possible from the foregoingdisclosure without departing from either the spirit or scope of thepresent invention.

We claim:
 1. An imaged printing plate formed by (a) exposing toradiation a negative-acting printing plate comprising a substrate havingcoated thereon a photosensitive composition comprising; (i) a reactive,acid functional polymer of the formula B(X)(Y), wherein B represents anorganic backbone, each X independently is an acidic group and each Yindependently is a photocurable group, and (ii) a photoinitiator whichinitiates crosslinking of said polymer upon exposure to said radiationto form a latent image-bearing article; (b) applying a fountain solutionon press to said latent image-bearing article without interveningdevelopment of the latent image-bearing article; and (c) thereafterapplying an ink to said latent image-bearing article, whereby an imagedprinting plate is formed from the latent image-bearing article on-press.2. The article of claim 1 wherein said photoinitiator generatesfree-radicals upon exposure to radiation.
 3. The article of claim 2wherein said photoinitiator generates free-radicals upon exposure toradiation between 300 and 850 nm.
 4. The article of claim 1 wherein saidphotoinitiator is selected from the group consisting of onium salts andphotolyzable organic halogen compounds.
 5. The article of claim 1wherein X is present in an amount of between 0.05 and 0.6 ephr, and Y ispresent in an amount of between 0.4 and 0.9 ephr.
 6. The article ofclaim 1 wherein X is present in an amount of between 0.1 and 0.4 ephr,and Y is present in an amount of between 0.45 and 0.8 ephr.
 7. Thearticle of claim 1 wherein said photosensitive composition furthercomprises free-radically polymerizable multi-functional monomer oroligomer.
 8. The article of claim 1 wherein the substrate is an aluminumsheet.
 9. The article of claim 8 wherein the substrate is an anodizedand silicated aluminum sheet.
 10. An imaged printing plate formed by (a)exposing to radiation a negative-acting printing plate comprising asubstrate having coated thereon a photosensitive composition comprising;(i) a reactive, acid functional polymer of the formula B(X)(Y), whereinB represents an organic backbone, each X independently is a salt of anacidic group and each Y independently is a photocurable group, and (ii)a photoinitiator which initiates crosslinking of said polymer uponexposure to said radiation to form a latent image-bearing article; (b)applying a fountain solution on press to said latent image-bearingarticle without intervening development of the latent image-bearingarticle; and (c) thereafter applying an ink to said latent image-bearingarticle, whereby an imaged printing plate is formed from the latentimage-bearing article on-press.
 11. The article of claim 10 wherein saidphotoinitiator generates free-radicals upon exposure to radiation. 12.The article of claim 11 wherein said photoinitiator generatesfree-radicals upon exposure to radiation between 300 and 850 nm.
 13. Thearticle of claim 10 wherein said photoinitiator is selected from thegroup consisting of onium salts and photolyzable organic halogencompounds.
 14. The article of claim 10 wherein X is a salt of a carboxylgroup.
 15. The article of claim 10 wherein X is present in an amount ofbetween 0.05 and 0.6 ephr, and Y is present in an amount of between 0.4and 0.9 ephr.
 16. The article of claim 10 wherein X is present in anamount of between 0.1 and 0.4 ephr, and Y is present in an amount ofbetween 0.45 and 0.8 ephr.
 17. The article of claim 10 wherein saidphotosensitive composition further comprises free-radially polymerizablemulti-functional monomer or oligomer.
 18. The article of claim 10wherein the substrate is an aluminum sheet.
 19. The article of claim 18wherein the substrate is an anodized and silicated aluminum sheet.